Britain's film censors have commissioned new research into public attitudes to depictions of sadistic and sexual violence in the wake of films such as The Bunny Game and The Human Centipede 2 which push, if not cross, boundaries of what is acceptable on screen.

David Cooke, director of the British Board of Film Classification (BBFC), said focus groups had already started watching some of the more extreme films. "We are asking the public on a fairly in-depth basis to look at some of this difficult material," he said. "We're really trying to get their take on whether the things they are seeing seem to them to be harmful or not."

It comes in the wake of films such as The Human Centipede 2 (Full Sequence) – in which a man achieves sexual gratification from stapling together his victims and which culminates in him raping a woman with barbed wire – and The Bunny Game, which mainly features the abduction, sexual abuse and torture of a prostitute by a truck driver. The latter film was refused certification by the BBFC while it asked for heavy cuts to the former in order to give it an 18 certificate.

The focus group will also watch Lars von Trier's Antichrist, the 2010 A Serbian Film (which has scenes depicting child rape and necrophilia), the 2008 film Martyrs (which contains sadistic violence) and the Michael Winterbottom film The Killer Inside Me – an example of a film that was abhorrent to some and critically praised by others.

Cooke said all members of the focus groups had been chosen carefully and would have access to counselling should they need it.

The last similar research was carried out a decade ago when the focus groups were watching films such as Straw Dogs and Death Wish 2.

Cooke said it was important to have a thoroughly researched policy on sexual violence, not least to use in the "fine-grained" arguments that would be heard should the BBFC be taken to court by a film-maker or distributor for refusing to award a certificate.

"We have a very strong repeat finding that the public expects us not to intervene at the adult level so that there is free choice, unless something is against the law or unless there is a harm issue. The most likely place to find a harm issue is sexual or sexualised or sadistic violence," he said.

Ipsos Mori is carrying out the research, the conclusions of which will be published later this year. "It will feed into our policies for intervention in these areas," said Cooke.

"I have no idea if it is going to produce a more interventionist policy or not. I find it quite difficult to imagine that the public is going to say there is no issue here, that we should just go away and ignore it all."

The announcement was made at the launch of the BBFC's 2011 annual report. Looking back, Cooke said there had been noticeably fewer complaints about films in 2011 and, perhaps surprisingly, it was Darren Aronofsky's psycho-sexual thriller Black Swan which had prompted the highest number, 40. "My theory is that this was a case of confounded expectations," Cooke said. "People maybe thought they were going to see a nice ballet movie."

The most complained about film this year, so far, is The Woman in Black, starring Daniel Radcliffe, which prompted 120 objections. It has a bit of a way to go to challenge the most complained-about film of the last decade: the Batman film The Dark Knight, which attracted just over 300 complaints, mainly about the sadism of Heath Ledger's Joker.

Cooke defended the board's policy on swearing in the light of criticism at the Cannes film festival from the team behind Ken Loach's The Angel's Share, who had to cut out several instances of the word "cunt". Writer Paul Laverty accused the BBFC of being obsessed with the word. "It is a word that the broad public opinion wants us to be vigilant about," said Cooke, and it was still "top of the charts" in terms of it being the worst swearword in the eyes of the broader public.

He admitted that the BBFC had trouble counting instances of the c-word in the film because there were "lots of quick and very fleeting uses".

Whether attitudes to swearing are becoming more tolerant will be put to the test next year in one of the BBFC's big public consultations of 8,000-10,000 people which it carries out every four or five years.

• This article was amended on 12 July 2012. We originally said the BBFC "banned" The Bunny Game and "insisted" on cuts to The Human Centipede 2. As a classifying agency, the BBFC can only refuse certification and request cuts to gain certification - it cannot forbid screenings. This has been corrected.